Silicon (Si), gallium arsenide (GaAs), and the like, are conventionally known semiconductor materials. Recently, the field of use of semiconductor elements is rapidly expanding. The semiconductor elements are accordingly more often used under severe conditions such as a high temperature environment. Achievement of a semiconductor element that is able to withstand a high temperature environment is one of important issues from the viewpoint of a reliable operation, processing of a large amount of information, and improvement in controllability in wide ranges of applications.
Silicon carbide (SiC) is of interest as one of materials that can be used for manufacturing a semiconductor element having an excellent heat resistance. SiC has an excellent mechanical strength and a radiation hardness. Adding impurities to SiC enables a valence electron such as an electron or a hole to be easily controlled, and SiC is characterized by having a large band gap width (3.2 eV in 4H monocrystalline SiC). For this reason, SiC is expected as a material for a next-generation power device that achieves a high temperature resistance, a high frequency resistance, a high voltage resistance, and a high environment resistance, which cannot be achieved by the existing semiconductor material described above. Patent Literature 1 to 3 (PTLs 1 to 3) disclose methods for manufacturing semiconductor materials with SiC.
PTL 1 discloses a method for manufacturing a high-quality SiC semiconductor, in which the temperature in a growth furnace for the growth of a seed crystal is made uniform so that generation of SiC polycrystals is suppressed. PTL 2 discloses a method for manufacturing a high-quality SiC semiconductor with less defects, in which a plurality of recesses are formed in a seed crystal.
Non-Patent Literature 1 (NPL 1) discloses Metastable Solvent Epitaxy (MSE) process which is a technique developed by the applicant of the present application. In MSE process which is a sort of solution growth technique, a seed substrate, a feed substrate having a higher free energy than that of the seed substrate, and an Si melt are used. The seed substrate and the feed substrate are arranged opposed to each other with the Si melt interposed therebetween, and in such a state, are heated under vacuum, so that monocrystalline SiC can be epitaxially grown on a surface of the seed substrate. In MSE process, there is no need to generate a temperature gradient in a monocrystalline SiC growth direction during heating, and epitaxial growth progresses due to a concentration gradient which is determined by a difference in the free energy. In MSE process, the seed substrate need not have an off-angle. PTL 3 discloses a method for manufacturing an SiC semiconductor using MSE process.